Magnetic amplifier with feedback



April 8, 1958 J. P. ECKERT, JR 2,830,196

MAGNETIC AMPLIFIER WITH FEEDBACK Filed March 4, 1955 2 Sheets-Sheet l FIG].

ee Pe'v Figs.4,5 01 6 B(Flux Denshy) MH (magnetizing Fore.) 27:95am"! lmpfidm a; I .Fl'6.5.

Feedback Imp cdo? Z Fmback Impedance Feedback Impedance FIG. 6

INVENTOR JOHN PRESPER ECKERT, JR.

April 8, 1958 J. P. ECKERT, JR

Filed March 4, 1955 MAGNETIC AMPLIFIER WITH FEEDBACK 7 FIG. 7.

2 Sheets-Sheet 2 Feedback Impedance Per Fiqs.5, 6 Or 8 Load l 93 98) Feedback Impedance Per Figs. 4, 5 0r 6 E g Load 4 i0 18/0.

Feedback Impedance Per Figs. 4,5 OrG I INVENTOR JOHN PRESPER EOKERT,JR.

AGENT MAGNETIC AMPLIFIER WITH FEEDBACK John Presper Eckert, In, Philadelphia, Pa., as signor, by mesne assignments, to Sperry Rand Corporation, a corporation of Delaware Application March 4, 1955, Serial No. 492,090

19 Claims. (Cl. 367-338) This invention relates to magnetic amplifiers and more particularly to increasing the output power from carrier type magnetic amplifiers. In the carrier type magnetic amplifier there is a series of high frequency power pulses fed through the power winding of a saturable core reactor. the core, each power pulse of the series drives the core from positive remanence to saturation. In the prior art, this situation is loosely described as operating the core under saturated conditions, while actually the core is never completely saturated and consequently the power pulses merely vary the core from one degree of partial saturation to a higher degree of partial saturation. If the core is at a still higher degree of saturation throughout the entire period of each power pulse, the output at the load will be still greaten It is a primary object of this invention to cause the core to operate under conditions of a greater degree of saturation throughout the entire period of each power pulse than has been customary.

It is another object of this invention to increase the power output of a magnetic amplifier.

A still further object of the invention is to increase the efiiciency of a magnetic amplifier.

In carrying out the foregoing objects, feedback means are employed whereby a small portion of the output current of the magnetic amplifier is fed into the input circuit with such polarity and at such time phase that it will retain the core between positive remanence and saturation during the spaces between pulses. Hence, instead of the core returning to positive remanence at the end of each power pulse, it returns only part way .in the direction of positive remanence. Each power pulse then drives the core from a point above positive remanence into the saturation region of the core. Since the core is above positive remanence at the start of each positive power pulse, it is driven farther into the saturation region than would be the case in the absence of the feedback means. As a result, the area of the hysteresis loop over which the core operates is smaller than would be the case in the absence of the feedback means.

in the drawings:

Figure 1 is a block diagram of a carrier type magnetic amplifier.

Figure 2 is a schematic diagram of one form of the invention.

Figure 3 is an idealized hysteresis loop for the core material of the magnetic amplifiers of this application.

Figure 4 illustrates one type of feedback impedance element that may be employed in connection with the invention.

Figure 5 illustrates another form of feedback impedance element that may be employed in connection with the invention.

Figure 6 illustrates still another type of feedback im pedance element that may be employed in connection with the invention.

In the absence of other magnetizing forces in nite States Patent Figure 7 is a schematic diagram of a modified form of the invention.

Figure 8 is still another form of feedback impedance element that may be employed in connection with the invention.

Figure 9 is a schematic diagram of still another modified form of the invention.

Figure 10 is a schematic diagram of yet another modified form of the invention in which a non-complementing magnetic amplifier instead of a complementing magnetic amplifier is illustrated.

Figure 1 is a block diagram of a carrier type magnetic amplifier which is not claimed herein as novel, inasmuch as similar ones are shown in several prior copending applications of the same assignee as the assignee of this application. For example, see the prior copending applications of Theodore H. Bonn and John Presper Eckert, Jr., Serial No. 446,095, filed July 27, 1954, now Patent No. 2,798,168, entitled Magnetic Amplifier and Flip- Flop Circuit Embodying the Same; John Presper Eckert, Jr., Serial No. 459,631, filed October 1, 1954, entitled Single Ended Carrier Type Magnetic Amplifier Bistable Device.

Briefly speaking, Figure 1 shows a magnetic amplifier fed by a carrier current and having an input wire B and an output wire C. The input is fed through filter E from an input terminal A and the output C is con nected to an output filter F connected to an output terminal D. If the feedback impedance element 28 of Figure 2 is eliminated, the circuit of Figure 2 would be a typical illustration of prior circuits. There now follows a brief description of the construction and mode of operation of the devices of Figures 1 and 2, assuming that the feedback impedance element 23 is omitted.

The core 20 of the magnetic amplifier may be made of a variety of materials, among which are the various types of ferrites and the various magnetic tapes, including Orthonik and 479 Moly-permalloy. These materials may have different heat treatments to give them difierent properties. The magnetic material employed in the core should preferably, though not necessarily, have a substantially rectangular hysteresis loop (as shown in Figure 3). Cores of this character are now well known in the art. In addition to the wide variety of materials available, the core may be constructed in a number of geometries, including both closed and open paths. For example, cup-shaped cores, strips, and toroidal-shaped cores are possible. Those skilled in the art understand that when the core is operating on the horizontal (or substantially saturated) portions of the hysteresis loop, the core is generally similar in operation to an air core, in that the coil on the core is of low impedance. On the other hand, when the core is operating on the vertical (or unsaturated) portions of the hysteresis loop, the impedance of the coil on the core will be high.

The source PP may generate a square wave alternating current of high frequency compared to the frequency of the pulses at the input 27. The pulses from source PP are fed through coil 21 and output filter 22 to the load 23. In the absence of input signals, the core 20 will be at positive remanence 30 (Figure 3) at the end and beginning of each positive-going power pulse. Each such power pulse will drive the core into a region of partial saturation, at say, 31, of Figure 3. Since the region 30-31 is a relatively saturated portion of the hysteresis loop, the coil 21 will have low impedance and substantially all of the potential of the source PP will appear at the load 23. A suitable smoothing filter 22 is placed in the output to convert the pulses into a continuous current with the ripple reduced to any desired extent. The operation will continue in this way until a negative signal appears at the input 27. Such a signal flowing through coil 24 will assume tend to revert the core during the spaces between positive excursions of source PF. This reversion constitutes driving the core from positive remanence point 30 to point 32 of the hysteresis loop. Each positive power pulse from source PP then drives the core to point 34 and, for small signal amplitudes, thence into saturation. Since this operating path includes an unsaturated portion of the hysteresis loop, the coil 21 will have hi h impedance while the core is operating on the said unsaturated por tion, and the current to the load 23 will be very reduced, in accordance with the input signal amplitude. When pulses pass through coil 21, they may induce in coil 24* high frequency potentials which would flow to the input 27, and which may disturb the input signal generator. To avoid this situation, an input filter, shown as filter E of Figure l and filter 25 of Figure 2, may be included in the input circuit. This filter allows currents at the frequency of the signals applied to input 27 to readily flow to coil 24, but substantially blocks the current due to the much higher frequency potentials induced in coil 24, due to the train of pulses passing through coil 21. Negative source 26 biases the anode of rectifier 26a negatively, and thus cuts off that rectifier except when an input signal is received at input 27 which has higher negative potential than the source 26. During negative excursions of source PP the anode of rectifier 29 is cut off and prevents flow of any current in coil 21 as a result of the changing flux due to flow of current in coil 24.

In accordance with the invention, a feedback is applied from the output of the carrier type amplifier to the input thereof. The feedback may be from wire C to wire B of Figure l, or from wire C to Wire A, or from output D to input A, or from output D to wire B. Figure 2 illustrates a complementing magnetic amplifier in which the feedback is from wire C of Figure l to input A. The

feedback element 28 in this case may be the simple resistor of Figure 4, a suitable inductor as shown in Figure 5, or a suitable filter as shown in Figure 6. For best results, the feedback means should cause the pulses at the output of coil 21 to arrive at the input coil 24 during the spaces between the positive pulses of source PP and should provide a magnetizing force on the core 20 which is in the same direction as that produced by coil 21.

It is noted that in the absence of the feedback means, the flux density in the core is at positive remanence 30 during the spaces between positive power pulses. With the feedback means, the core would be at a greater degree of saturation, say 35, during the spaces between positive pulses of source PP. This is accomplished in Figure 2 by reason of the fact that a current is fed back through the impedance element 2%, thence through filter 25 to the coil 24, and thence through the coil 24 in the same direction as the positive pulses from source PP are fed, through the coil 21. The feedback impedance element 28 and the input filter 25 are so related that they provide suficient delay that a pulse leaving the coil 21 arrives at the coil 24 during the space following that or some succeeding pulse. In other words, it is preferable but not necessary, that the pulse leaving coil 21 be delayed just enough so that when it arrives at coil 24 it fills the gap between itself and the next succeeding pulse from source PP, but it may be delayed to fill any subsequent gap between positive excursions of source PP. In many cases the input filter 25 taken alone will provide sufficient delay. Moreover, in all cases it is not necessary that the pulse, after being delayed, still be in the form of a pulse as the inductor and the condenser of the filter may smooth out and elongate the pulse somewhat so that it is of greater duration than the space between power pulses.

If all or part of the delayed pulse arrives at coil '24 during a space between two positive excursions of source PP, the desired result will at least partially be achieved. In event the input filter 25 provides sufficient delay, the

feedback element 28 may be a simple resistor, as shown in Figure 4. If the input filter 25 does not provide sufficient delay to achieve best results, a feedback element having some energy storage characteristics may be employed, such as the inductor of Figure 5. It is also feasible to use a smoothing filter, as shown in Figure 6, as this will provide a steady direct current through the coil 24 and will thus partially positively magnetize the core during the spaces between positive excursions of source Pi. When the feedback element 28 is included in the circuit, the core 20 instead of returning to positive remanence 36 at the end of each positive excursion of source PP, will return to a higher degree of saturation, say point 35, of Figure 3. Each positive excursion of the source PP will then carry the core to, say point 36 of the hysteresis loop, which is higher than the point 31 (the latter being assumed to be the point where the core would be driven in the absence of the feedback element). Therefore, without the feedback element, the core will be driven along the portion 3tl3l whereas with the feedback element the core will be driven along the portion 35--36. Since the latter portion involves a greater saturation of the core than the former, the output is increased by use of the invention.

In event an input signal is received at input 27, it will flow through the coil 24 and tend to revert the core, the same as is true in connection with the circuit without the feedback element 28. In that case, the next positive excursion of the source P-P will occur along relatively unsaturated portions of the hysteresis loop.

In devices embodying the present invention, the number of volt-seconds of the power pulses of source PP is less critical than heretofore. Heretofore it has been con sidered desirable for each positive power pulse ,to be capable of driving the core 20 from point 33 to point 34 (Figure 3). With the present invention, this is not necessary since if the power pulses are not that effective, the feedback means will insure that after several cycles have elapsed the core is always at 30 or some higher point on the hysteresis loop at the start of each power pulse.

Figure 7 is a modified form of the invention, where the feedback element is connected from point C to point B of Figure 1. In this case, since neither of the filters E or F is included in the feedback circuit, the feedback element 78 must have an inherent delaying characteristic. The feedback elements of Figures 5, 6 and 8 have delaying characteristics and may be used in Figure 7. The input 77 of Figure 7 corresponds to input A of Figure 1; the filter of Figure 7 corresponds to filter F. of Figure l; the magnetic amplifier 7t), 71, 74, 76 corresponds to the magnetic amplifier of Figure l and to the amplifier 20, 21, 24, 26 of Figure 2; the output smoothing filter 72 of Figure 7 corresponds to filter F of Figure l; and the load 73 corresponds to the load D of Figure 1. In Figure 7 the feedback impedance element 78 delays the pulses leaving coil '71 to a sutficient extent that they arrive at the input coil '74 during the spaces between positive excursions of source PP, and thus raises the core 70 above positive remanence during the spaces between power pulses and leaves the core at a point, say 35 on the hysteresis loop of Figure 3, at the beginning of the next positive excursion of source PP so that the core is driven farther into the saturation region than would be the case in the absence of feedback impedance element 78.

Figure 9 is a circuit diagram of a modified form of the invention in which the feedback takes place from the out put D of Figure 1 to the input A. In Figure 9 the input 97 corresponds to the input A of Figure 1, the inductor corresponds to the input filter E of Figure l, the magnetic amplifier 90, 91, 94, 96 of Figure 9 corresponds to the magnetic amplifier of Figure 1 and to the magnetic amplifier 20, 21, 24, 26 of Figure 2. The output filter 92 of Figure 9 corresponds to the output filter F of Figure essence l and the load D of Figure 1 corresponds to the load 93 of Figure 9. In this case the smoothing filter 92 plus the input filter 95 tend to smooth out the pulses leaving power winding 91 so that the feedback element 98 need not have any delaying characteristics of its own. Hence, the simple resistor of Figure 4 may be used. However, the more complex feedback elements of Figures 5, 6 and 8 may be used if desired. in any event, when the amplifier is in the output producing state, the output current arrives at input coil 94 during the spaces between positive excursions of source PP and holds the core at, say point 35 of the hysteresis loop of Figure 3, during these spaces and leaves the core at point 35 at the beginning of each positive excursion of source PP.

The foregoing figures have shown the invention applied to complementing magnetic amplifiers. it is equally applicable to amplifiers of the non-complementing type. Such an amplifier is shown in Figure 10. Its construction and mode of operation will now be described, assuming that the feedback element its is absent. Each positive excursion of source PP flows through rectifier )9, power winding 161 to the output filter 362 and then to the load 103. This tends to magnetize the core in the positive direction. However, during the spaces between positive power pulses, current from negative source 89 flows through resistor 3h, coil 101 and rectifier 87, thus applying a negative magnetizing force to the core. Consequently, during positive excursions of source PP, the magnetizing force in the core is positive and during the negative excursions of source PP the core has a negative magnetizing force therein. Hence, at the beginning of each positive excursion of source PP the core 1% is at negative remanence 33 and the power pulse drives it along an unsaturated portion so that there is very little output from the coil lltli. This situation will continue until a pulse is received at the input 107. if, during one or more negative excursions of source PP, a positive pulse appears at input 107, current will flow from source 1657 through rectifier 86, input filter 1'05, and input coil 1M, and establish a magnetizing force opposite to that established by source 89. Hence, the magnetizing force on the core due to the positive excursions of source PP will drive the core into saturation and thereafter each individual pulse will drive the core to positive saturation region 31, whereby the coil 101 will have low impedance and there will be a large current fed to the filter 192 and thence to the load 103. The filter M2 may be designed to reduce the ripple in the load current to any desired extent. In any case, the potential induced in coil 1M due to the pulses flowing in coil 101 may not flow to the magnetizing force of source 89 and the core will be at a more positive flux density operating point prior to the application of each power pulse than would be the case in the absence of the feedback. Hence, the core operates in a more saturated region than is normally the case with carrier type amplifiers, thereby producing greater gain than has heretofore been the case.

While this invention has been described and illustrated with reference to a limited number of specific embodiments, it is to be understood that the invention is capable of various other modifications and applications, not departing essentially from the spirit thereof, which will become apparent to those skilled in the art.

I claim to have invented:

1. In a carrier type magnetic amplifier, a saturable core, winding means on the core, said winding means having an output, means for feeding power pulses through said winding means to said output, input means controlling the reversion of the core, said power pulses having a high repetition rate compared to the repetition rate of the input signals, and regenerative feedback means for feeding current from the output to the input means in such amplitude, phase and polarity as to effect an increase in the output power as compared to what the output power would be in the absence of the regenerative feedback means.

2. in a carrier type magnetic amplifier, a saturable core, a power winding on the core, means connected to one end of the power winding to feed it with spaced power pulses tending to drive the core to partial saturation in the absence of reversion of the core during the spaces between pulses, an input means for rejecting pulses at the repetition rate of the power pulses but passing lower frequency input signals to control the reversion of the core, and regenerative feedback means for feeding part of the current reaching the other end of said power winding into said input means in such direction and phase as to increase the degree of saturation of the core.

3. in a carrier type magnetic amplifier, a saturable core, a power winding on the core, means connected to one end of the power winding to feed it with spaced pulses tending to drive the core to partial saturation, input means controlling the reversion of the core during the spaces between pulses, and a feedback path connecting the other end of the power winding to the input means to supply the latter with current tending to increase the degree of saturation of the core, said feedback path including delay means for delaying the application of the feedback current so that output current from the power winding arrives at the input means during a space between said pulses, the first named means producing its power pulses at a high repetition rate as compared to the repetition rate of the input signals.

4. In a carrier type magnetic amplifier, a saturable core, winding means on the core, a source of spaced pulses, means for feeding said pulses through at least a part of the winding means to at least partially saturate the core in one direction unless the core is reverted during the spaces between pulses, an input, and means connected to both said input and to said winding means for reverting the core in response to predetermined conditions at the input and for driving the core toward saturation in said direction during the spaces between pulses in the absence of said predetermined condition at the input; the last named means including an input filter which blocks flow of current, at the repetition rate of the power pulses, from the winding means to the input while allowing pulses of repetition rate slower than the power pulses to pass to the winding means for controlling the reversion of the core.

5. In a non-complementing magnetic amplifier, a saturable core, winding means on the core, a source of spaced pulses for feeding current through at least a part of the Winding means to at least partially saturate the core in one direction unless the core is reverted during the spaces between pulses, an input, and means connected to both said input and to said winding means for reverting the core during the spaces between pulses in the absence of an input signal and for maintaining the core beyond remanence toward saturation in said direction during the spaces between pulses in the presence of the input signal.

6. In a non-complementing magnetic amplifier, a saturable core, winding means on the core having input and output terminals, means for passing a series of spaced pulses through at least a part of the winding means to the output terminal to at least partially saturate the core unless it is reverted during the spaces between pulses, reverting means connected to the winding means for re? verting the core during the spaces between pulses, and feedback means connected to the output terminal and t the input terminal for supplying a current to the input terminal tending to partially cancel the effect of the reverting means during the spaces between pulses so that an input pulse during said spaces will cause the output current to have greater amplitude than it would have in the absence of the feedback means.

7. in a complementing carrier type magnetic amplifier, a saturable core, winding means on the core having an output, means for feeding a series of spaced pulses through at least a part of the winding means to th output, said pulses having such amplitude as to drive the core to one of its saturation regions unless it is reverted during the spaces between pulses, an input, an input filter connecting the input to the winding means so that input signals will revert the core, said input filter being tuned to block flow of current at the pulse frequency toward the input, a load, an output filter connecting said output to the load and smoothing the pulse output to a continuous current, and feedback means connecting said output to said input, said input filter tending to delay some of the output current and feeding it to the winding means during the spaces between pulses in proper direction that it tends to drive the core toward said one saturation region.

8. In a complementing carrier type magnetic amplifier, a saturable core, winding means on the core having an output, means for feeding a series of spaced pulses through at least a part of the winding means to the output, said pulses having such amplitude as to drive the core to one of its saturation regions unless it is reverted during the spaces between pulses, an input, an input filter connecting the input to the winding means so that input signals will revert the core, said input filter being tuned to block flow of current at the pulse frequency toward the input, a load, an output filter connecting said output to the load and smoothing the pulse output to a continuous current, and feedback means connected at one end to said output and at its other end to the end of tie input filter that is connected to the winding means, the feedback means including a delay element for delaying the output current whereby it arrives at the other end of the feedback means during spaces between power pulses.

9. In a complementing carrier type magnetic amplifier, a saturable core, winding means on the core having an output, means for feeding a series of spaced pulses through at least a part of the winding means to the output, said pulses having such amplitude as to drive the core to one of its saturation regions unless it is reverted during the spaces between pulses, an input, an input filter connecting the input to the winding means so that input signals will revert the core, said input filter being tuned to block fiow of current at the pulse frequency toward the input, a load, an output filter connecting said output to the load and smoothing the pulse output to a continuous current, and feedback means for feeding current from the load end of the output filter to the input.

10. In a complementing carrier type magnetic amplifier, a saturable core, winding means on the core having an output, means for feeding a series of spaced pulses through at least a part of the winding means to the out put, said pulses having such amplitude as to drive the core to one of its saturation regions unless it is reverted during the spaces between pulses, an input, an input filter connecting the input to the winding means so that input signals will revert the core, said input filter being tuned to block flow of current at the pulse frequency toward the input, a load, an output filter connecting said output to the load and smoothing the pulse output to a continuous current, and feedback means for feeding current from the load end of the output filter to the winding means in such direction as to drive the core toward said saturation region.

.11. In a carrier type complementing magnetic amplifier, a saturable core having separate windings constituting power and input windings, a source of spaced power pulses connected to one end of the power winding, a smoothing filter connected in series with the other end of the power winding, an input, an input filter connected at one end to the input and at its other end to the input winding, and regenerative feedback means feeding part of the current that flows through the power winding to the input winding to produce a magnetizing force during the spaces between pulses that is in the same direction as that produced by the power winding and o osite .0 that produced by an input signal.

A carrier type complementing magnetic amplifier as defined in claim 11 in which one end of the feedback means is connected to said other end of the power winding ahead of the smoothing filter and has its other end connected to the input side of the input filter, said t filter allowing input signals to fiow to the input winding while blocking fiow of current at the frequency of said spaced pulses from the input winding to the input and delaying the feedback current so that the pulses leaving the power winding arrive at the input winding during the spaces between pulses.

13. A carrier type complementing magnetic amplifier as defined in claim 10 in which one end of the feedback means is connected to said other end of the power winding ahead of the smoothing filter and has its other end connected to the end of the input filter that is connected to the input winding, the feedback means including a delay element for delaying the pulses leaving the power winding so that they arrive at the input winding during the spaces between pulses.

14-. A carrier type complementing magnetic amplifier as defined in claim 10 in which one end of the feedback means is connected to the output side of the smoothing filter and its other end connected to said input, the smoothing filter and the input filter delaying the pulses fed through the power winding so that current flows through the input winding during the spaces between pulses.

15. A carrier type complementing magnetic amplifier as defined in claim 10 in which one end of the feedback means is connected to the output side of the smoothing filter and the other end feeds the input winding, the smoothing filter delaying the pulses fed through the power winding so that it arrives at the input winding during spaces between pulses.

16. In a carrier type non-complementing magnetic amplifier, a saturable core having separate windings constituting power and input windings, a source of spaced pulses feeding one end of the power winding, a smoothing filter connected to the other end of the power winding, an input, an input filter connecting the input to the input winding and allowing input signais to flow from the input to the input winding while blocking current at the frequency of the pulses from flowing from the input winding to the input, means for passing a reverting current through one of said windings during the spaces between pulses, and regenerative feedback means for feeding some of the current that passes through the power winding through the input winding during the spaces between pulses to at least partially cancel the effect of the reverting current.

17. In a carrier type magnetic amplifier, a saturable core, winding means on the core having an input and an output, a source of spaced power pulses for passing current through at least a part of the winding means to said output, said power pulses driving the core into partial saturation unless the core is reverted between pulses, and regenerative feedback means which when the amplifier is in an output producing condition feeds current to the input and holds the core above remanence so that it is driven farther toward saturation and reaches predetermined degrees of partial saturation quicker than would be the case in the absence of the regenerative feedback means.

18. A carrier type magnetic amplifier as defined in claim 17 in which the repetition rate of the power pulses is high compared to the frequency at which the core is reverted, and input means for reverting the core including a filter which blocks signals of the repetition rate of said power pulses while allowing the input pulses to pass.

19. In a carrier type magnetic amplifier, a saturable core, winding means on the core having an input and an output, a source of spaced power pulses for passing current through at least a part of said winding means to said output, said power pulses driving the core into par- 10 tial saturation unless the core is reverted between pulses, said power pulses having a high repetition rate compared to the frequency at which the core is reverted, an input filter tuned to reject signals having the repetition rate of said power pulses and feeding said winding means with signals for controlling the reversion of said core, and feedback means fed by said output for effecting a magnetomotive force in the core in the same direction but of smaller magnitude as that due to the power pulses fed to the input of the winding means and occurring in the intervals between said power pulses.

References Cited in the file of this patent UNITED STATES PATENTS 2,164,383 Burton July 4, 1939 2,574,438 Rossi et a1 Nov. 6, 1951 2,677,097 Carleton Apr. 27, 1954 2,709,798 Steagall May 31, 1955 

